1. Field of the Invention
The present invention relates to a switchgear control apparatus for controlling opening/closing operation of each circuit breaker of a switchgear for connecting a three-phase reactor having a three-phase core to a three-phase AC power source and, more particularly, the invention is concerned with a technique for suppressing inrush currents which may occur when the three-phase reactor is energized.
2. Description of the Background Art
Conventionally, a controlled switching technique is used for suppressing inrush currents which can occur when a three-phase reactor is energized. For example, PCT International Patent Application Republication No. WO0004564 discloses as a fifth embodiment thereof a switchgear control apparatus for suppressing excitation inrush currents. Specifically, when supplying a source voltage to a shunt reactor having a three-phase core and star-connected windings whose neutral point is grounded, the switchgear control apparatus suppresses the excitation inrush currents by first supplying the source voltage to a first phase (R phase) at a point where a first-phase voltage is at a maximum and then supplying the source voltage to second and third phases (S and T phases), thereby preventing transient phenomena.
In the conventional controlled switching technique, a target phase angle at which a voltage to each phase of a three-phase reactor is supplied is determined on the assumption that residual magnetic flux in a reactor core is at zero level. In practice, however, a slight amount of residual magnetic flux remains in the reactor core. In addition, as the residual magnetic flux reaches maximum levels randomly in the three-phase reactor core of the individual phases, the conventional controlled switching technique is not effective enough in suppressing the inrush currents.